Processing hydrocarbon oils



Oct. 10, 1939.

1K. ROBERTS Er AL PROCESSING HYDROCARBON OILS Filed May 29, 1957 2 Sheets-Shet 1 Oct. l0, 1.939. 1 K, ROBERTS E -r AL 2,175,362

PROCESS ING HYDROCARBON OILS Joy ATTORNEY Patented Oct. 10, 1939 PROCESSING HYDROCARBON OILS Joseph K. Roberts, Flossmoor, and Jay H. Forrester and Roys@ Diwoky, Chicago, Ill., assignors to Standard Oil Company, Chicago, Ill., a corporation oi' Indiana A Application 1May 29,193mseria1 No. 145,468

UNITEDSTATES PATENT OFFICEr 3 Claims. (Cl. 19E-48) fractions with a minimum cost for fuel and equipment. Still another object of the invention is to improve the operation of the cracking unit by a novel means of control wherein the charging rate to the unit is maintained constant.. Still another object of the invention is to operate two or more cracking units in unison connected to a common furnace oil stabilizer where the furnace 'oil fraction is distilled by its contained heatto remove undesirable gases'. The furnace oil containing gasoline constituents may'then be subjected to chemical treatment and redistilled to produce the desired boiling range and' obtain at the same time a chemically treated gasoline fraction which may be blended for the production of a special grade of gasoline. Other objects of the invention will be apparent from the following description.

The drawings which form a part of this specification show diagrammatically an arrangement of two or more cracking units coupled in parallel with separate common discharge lines for gas, gasoline, furnace oil and tar and with combined stabilizing equipment for furnace oil and gasoline. Figure 2 is an extension of thediagram shown in Figure 1. The invention will be readily understood by reference to the drawings and the following description thereof.

Referring to the drawings, A and B are members of a series of cracking units, A, B, C, `D, etc., only two of whichare shown. The cracking units are connected by furnace oil header line I0 and gasoline header I I to furnace oil stabilizer I2 and gasoline debutanizer I3 respectively. A stabilizing column I4 is provided to remove undesirable propane and otherilxed gases from the gasoline aridlight constituents obtained as a disytillate fromthe furnace oil stabilizerv and the '.debutanizerlw "',Tary flash drum I5 is provided to -@receivethe hot tar from all the cracking units `and dis l it by contained heat, thereby removingngasolvneand other lighter fractions. The gasolineglcontaining distillate removed from the .tar maybefreturned as reflux t'othe fractionating towers of the cracking units A, B, etc.,

through reiiux header I6.

In'conducting the' operation we prefer to charge Mid-Continent gas oil having about the following boiling range: 5

Initial l 29o 50% a 652 65% '10o 81% n -v5o 1o This stock, hereinafter called fresh feed, is introduced thrpughheader I1 by pumps not shown. From the header I1 thefresh feed is withdrawn through line I8 and reflux exchanger I9 to line leading to cracking coils 2l and 22, in furnace 23. If desired, a portion of the fresh feed may be directed through line 24 into the top ofthe evapv orator 25 to serve as reflux therein. A portion may also be withdrawn through line 26 directly 2o into vapor line 21 for the purpose of cooling and fluxing this line and preventing formation of coke therein.

At the point of entering coil 22 in furnace 23 the fresh feed may be commingled'with recycle stock withdrawn from fractionator 28 by line 28a as' hereinafter described. The combined fresh feed and recycle oil in passing through furnace 23 is heated to a higher temperature in the range of 900-1000 F. where it is substantially all vaporized. The hot vapors are conducted by transfer line 29 to soaking drum 30 and thence by line 3l to evaporator 25. A considerable proportion of the oil is converted to lower boiling hydrocarbons in the furnace 23 and in soaking drum 30. Thepressure in the' soaking drum may 35 suitably'be from 100to 400 lbs. per sq. in. under which conditions the oil will besubstantially all in the `vapor phase. The hot vapors are partially condensed by reiiux cooling in evaporator 25 and a heavy tar fraction is withdrawn therefrom 4 by tar drag line 32 connected to tar header 33.

The vapors in evaporator 25 are conducted by A line 21 to fractionator 28 where they are further cooled and fractionated to remove the gasoline constituents and an intermediate fraction) herein called furnace oil distillate. Gasoline` vapors are withdrawn from the fractionator by vapor line 3l leading to condenser 35 wherefall the gasoline is condensed and conducted with separated gases to separating drum 36. Vent 31 connects the separating drum to thedry gas header 38 and distillate discharge line 39 'simil larly conducts the gasoline from separator v36 to distillate header Il. 'I'he gas discharged 'into 55 header 38 may be substantially free from gasoline, in which case it is discharged from the system to be used as fuel gas or burned in the furnaces, A, B, etc. The pressure in the fractionator 28 may be approximately the same as that in the soaking drum 30 and evaporator 25. If desired, however, the pressure may be reduced in the evaporator 25 and/or the fractionator 28 by placing valves in lines 3I and 21. Thus a pressure of to 100 lbs. may be conveniently maintained in evaporator 25 and/or fractionator 28.

As the hot vapors ascend fractionator 28-they are cooled by reflux from reflux exchanger I9 and also from reflux line 40 connected to reux header I6. As a result of the cooling heavy uncracked constituents together with partially cracked constituents of the gas oil originally charged are cony through lines 20 and 28a which may be accomplished by keeping the operation of the fresh feed Dump (not shown) and the recycle pump 46 substantially constant, Any variation in the extent of cracking due to change in temperatures, na-

, ture of feed stock, and other conditions may be compensated for by withdrawing a greater or lesser amount. of furnace oil stock from the midportion of fractionator 28.- As a. result much more uniform operation of the cracking unit is obtainable and higher through-put results. Uniform charge to furnace 23 also facilitates the con- Y operating with a fresh feed rate of 150 bbl/hr.

, the furnace oil distillate withdrawal may be about 20-50 bbL/hr. or 30 bbl./hr. in a typical instance.

is c'onductedby line 41 to vfurnace oil stabilizer I2 where it is introduced at a temperature of about 580600 F. The pressure is reduced by valve 48 to about 90 lbs/sq. in., thus causing the i evaporation of a light gasoline and gas fraction,

theV vapors being withdrawn by line 49 through cooler 50 and thence to accumulatordrum 5I. Reflux condensate .may bel returned to the stabinzer lz'by reflux line 52. The stabilized fur-- nace oil distillate is withdrawn from the base of stabilizer I2 by line 53 -leading to cooler 54 and." furnace oil distillate tank 55. This stock may have thelfollowing distillation range:

F. Initial 270 20% 377 50% 429 Maximum y 576 Gasoline distillate withdrawn from the base of -denser 63 and stabilizer feed tank 64.

the separator 36 by line 39 -to distillate header II is conducted by line 56 to feed tank 51 whence it is led by line 58 through heater 54 into debutanizer column I3. In the column I3 there is removed .from the gasoline distillate most of the butane, together with some pentane and heavier constituents and substantially all propane and lighter hydrocarbons at a pressure of about 50 to 125 lbs. per square in ch. Vapors of these light hydrocarbons are conducted by line 59 through condenser 69 and into reflux accumulator 5I whence suilicient condensate is withdrawn by lines 52 and 6I to supply the desired reflux in column I3. Uncondensed gases are Withdrawn from accumulator 5I by line 62 leading to con- Uncondensed vapors are withdrawn from tank 64 by line 65, and combined with vapors from feed tank 51 discharged by line 66. The combined vapors .are conducted to absorber 61 where some propane and substantially all the butane and heavier gasoline hydrocarbons are recovered in an absorber oil introduced by line 68 and discharged to a suitable gasoline recovery system by line 69. The unabsorbed gases are discharged by line 10 leading to fuel gas header 38.

Liquid butane and'other light hydrocambons.`

condensed in tank 64 are withdrawn by line 1I leading to stabilizer I4 where propane and lighter hydrocarbons are separated under pressure from butane and heavier desired gasoline constituents. The Apressure in I4 may beabout 150 to 350 lbs. per sq. inch.- The vapors are conducted from stabilizer I4 through a suitable reflux exchanger 1 12 and reflux drum 13 whence the uncondensed vapors are discharged to the fuel line by line 14. Reflux is supplied to the stabilizer I4 by line 15.

Heat for operating stabilizer tower I4 is supplied by heater' 16 through which is circulatedliquid trapped from the tower by line 11 and returned thereto by line 18. Stabilized liquid is withdrawn from tower I4 by line 19 and conducted to storage tank 80. n

The debutanizer column I3 may be supplied with heat-from heater 8| in a manner similar to that employed for heating stabilizer I4. Heat for heaters 16 and 8| may be conveniently obtained by circulating a stream of hot tar therethrough. Hot furnace oil distillate from header III may likewise be used for this purpose o'r we may also use recycle gas oil from tower 88.

Debutanized gasoline from the base of tower I3 is withdrawn by line 82 through cooler 83 and thence by line 84 to debutanized gasoline storage tank 85. This gasoline distillate is substantially free from heavier hydrocarbons boiling above the gasoline range'. For example, it may have a boiling range as indicated by the following A. S. T. M.l

distillation: u F Initial 14s' 50% 260 339 Maximum 397 ItA maybe withdrawn from receiver 8l by line -IOII and sweetened by treating with sodium plumbite or other sweetening reagent in plant IIII- .(Fig'ure 2) to remove malodorous sulfurous compounds and thereafter it may be treated with .an antioxidant to prevent gum formation in to storage in tank I 03,' No chemical refining with sulfuric acid is necessary nor is it necessary to 16 subject this distillate to redistillation before blending to make finished motor fuel. To obtain gum stability we may add about .002% to .005% of monobenzyl aminophenol or other suitable gasoline antioxidant. y

Hot tar which is withdrawn from evaporator 25 and the other evaporators of the cracking units A, B, etc. is conducted through tar lines 32, tar header 33 and line 85 to tar flash tower I5 where it is distilled by its contained heat and the vapors are conducted by line 8l to fractionator 88 where it may be divided into several fractions as desired. The light distillate from fractionator 88 may be conducted by line 89 to condenser 90 and separator 9| whence the liquid is withdrawn by line 92 to reflux accumulator 93.

Here it may beblended with other light distillate introduced by line 94 and the mixture is then conducted by line to reflux header I5. By operating in this way the gasoline constituents of the tar find their way back to the fractionating column 28 and also light constituents of the tar which are desired in the furnace oil find their way to the furnace oil stream withdrawn from the fractionating tower by line 42. Unvaporized con-l stituents of the tar are withdrawn from flash tower I5 by line 96' and may be treated to produce satisfactory heavy fuel oil, for example by hot ltration or other suitable method of -treatment. Additional tar distillate fractions may be withdrawn from suitable trap-out plates not shown and from the base of fractionator 88 by line 91 as desired.

Stabilized furnace oil distillate collected in receiver 55 may be withdrawn by line I 04 and treated with sulfuric acid in the usual'manner in plant |05 and redistilled in |06 to produce stable light and heavy gasoline fractions and a furnace oil fraction. A tractor fuel fraction may also be separated. These may have about the following distillations: Y

Light Heavy Tractor Furnace gasolinel gasoline fuel oil F. F. F. Initial 112 250 358 358 50 percent. 242 385 423 452 percent.. 31 382 471 489 Maximum 374 420 512 5.50

tion from furnace oil distillate may likewise require no antioxidant for gum stabilization.

The stabilized light gasoline and heavy gasoline in receivers 80 and 85 may be blended byline |01 in proper proportion to produce a motor fuel having the desired volatility. For example, 30- volumes of stabilized light gasoline may be blended with 70 volumes of stabilized heav'y gasoline to produce a motor fuel having a Reid vapor pressure of 11.8 pounds and a volatility indicated by the percent distilled at 158 F. of 24.3%. The composition, of the stabilized light gasoline in tank 80- may be varieddepending on the conditions of operating debutanizer I3. Thus, by operating debutanizer I3 at a higher temperature more light gasoline 4will be produced having a lower volatility.

One of the advantages of our process is the unified stabilization system for both gasoline and furnace oil distillates represented by towers I2,

I3 and I4. The operation of unit stabilization of this character is made possible by the manifolding of a. large number of cracking units, for example 5 or 10 units, thus providing a relatively constant supply and composition of feed stocks for the vunit stabilization system even when one or more of the units are shut down temporarily for cleaning. Another advantageof our process which has been mentionedhereinbefore is the improved control of the cracking operation by trapping out of the fractionator a variable amount of furnace oil distillate which would otherwise be recycled in the unit. Regulation of the -cracking unit by regulating the withdrawal of furnace oil distillate from the fractionator controls the balance between the furnace, -evaporator, the fresh feed charging stock, the recycle stock and the fractionator. The result is a. smoother operation than has been heretofore obtainable. l

Still anotheradvantage of the process is the return of light distillate from the tar to the cracking unit fractionators as reux where heavier portions are fractionated and withdrawn with the furnace oil distillate stream without any further crackingor imposing any additional duty on the cracking coil.

To still further aid in balancing the operation v of the cracking units and maintain desired in ventories of refinery stocks, a part, or at times, all of the furnace oil may be blendedwith the charging stock to the units. This, however, results in making the stock somewhat more refractory, since elimination of the furnace oil results in increasing the paraiiinicity of the charge to the vcoils and thereby increases gasoline producing capacity.

tionated under pressure in a fractionating zone from which gasoline vapor is withdrawn at the top, incompletely cracked lhydrocarbons are condensed and withdrawn at the bottom whence they are recycledto 'said cracking zone, and an intermediate boiling furnace oil condensate contain- .ing dissolved gasoline is withdrawn from an intermediate point of said fractionating zone, the improvement comprising conducting said furnace Oilcondensate to a second fractionatingzone at lower pressure where dissolved gasoline is septhe Aresidue in said fourth fractionating zone also substantially free from propane to produce a suitable stabilized motor fuel product.

3. The process of obtaining uniform operation in a battery of cracking units wherein each unit is supplied from common headers with fresh feed stock, fuel and fractionating tower reflux and each unit is likewise arranged to discharge gasoline distillate, gas, furnace oil condensate and tar into other suitable common headers, and wherein one or more units is periodically shut down temporarily for cleaning while the remaining units continue operating, comprising combining furnace oil condensate from al1 operating units and distilling gases and dissolved gasoline therefrom in a first single fractionating zone by the contained heat of said condensate, combining gasoline distillates from all units and distllling therefrom a light fraction including all the propane in a second single fractionating zone, combining the overhead fractions thus obtained from said first and second fractionating zones and sub jecting them to further fractionation under pressure to separate gasoline from propane and lighter hydrocarbons, and regulating the rate of withdrawing furnace oil condensate from each unit to maintain a constant rate of fresh feed charged thereto.

JOSEPH K. ROBERTS.

JAY H. FORRES'I'ER.

ROY J. DIWOKY. 

